The invention relates to a method comprising the steps of:
A) determining a quantity related to a person""s personal minimum erythema dose (MED), and
B) using said quantity as an input for a tanning-related device, thus influencing its operation.
Tanning is induced by irradiation with ultraviolet (UV) light, either from natural sunlight or from a solarium. As is known, large doses of ultraviolet light are harmful. However, the dose that is harmful differs from one person to the next and even from one time to another for a single person.
The parameter currently used to quantify a person""s sensitivity to ultraviolet light is the minimum erythema dose (MED), the smallest dose that induces visible redness of the skin. In order to avoid radiation damage, it is generally accepted that this MED should not be exceeded. For efficient tanning, on the other hand, a person wants as high a dose of ultraviolet light as possible. The problem is that the person does not know his MED exactly. Currently, MED can be estimated or measured.
Estimation of MED makes use of the skin type classification (types I-VI, where the users of solaria will almost exclusively fall into types II-IV). Skin type classification is based on visual inspection and on a questionnaire with questions about personal sunburn and tanning experiences. However, substantial errors can be made, and often the skin type cannot be established unambiguously. Because of this uncertainty, it is always advised to stay on the safe side. Many people will therefore start their tanning programs sub-optimally, i.e. with doses that are lower than what they could safely receive.
Measurement of MED involves exposing a series of small patches of skin to increasing doses of ultraviolet light. The lowest dose that induces visible redness is the MED. This measurement is very reliable, but inevitably involves radiation damage to the skin. It is unpleasant, should not be performed repeatedly on the same person, and must always be carried out by a dermatologist. For this reason, such measurements are only suitable for medical purposes and not for use with consumer products.
It has been discovered that a relatively accurate correlation between non-invasively determinable features of the skin and MED exists, as disclosed by L. S. Matchette of the Center for Devices and Radiological Health, of the US Food and Drug Administration, at the 13th International Congress on Photobiology in San Francisco, Calif. By using this correlation one can predict a person""s MED without inducing damage to the skin. Thus, there is no objection to repeated measurements by a non-schooled user. The invention aims at benefiting from the advantages offered by this kind of non-invasive determination of a person""s personal MED.
According to the invention, this is achieved by a method comprising, for the purpose of step A), the steps of:
C) non-invasively measuring a feature of the person""s skin related to the person""s personal MED, and
D) electronically deducing the person""s personal MED from the measured feature.
According to this method it is possible to use information coming from an objective measurement with no risk of skin damage for controlling a tanning-related device. The tanning-related device to which the output signal is provided could be, for example a dosimeter, for example as part of a solar watch, which measures overall light intensity and warns the user when he has probably received a too high sunlight dose. Another suitable tanning-related device is a solarium, which could be switched off automatically when the person has reached his MED.
Advantageously, the light attenuation in the skin is measured during step C). It has been discovered that a relatively good correlation between said attenuation and MED exist.
The light attenuation in the skin can be measured by using optical coherence tomography, which is an imaging technique which is known per se by those skilled in the art, based on low-coherence interferometry, which technique can also be used for the measurement of the light attenuation. The principle of optical coherence tomography is described, for example, in D. Huang et al., xe2x80x9cOptical Coherence Tomographyxe2x80x9d, Science 254, 1178 (1991), and optical coherence domain reflectometry is described in B. L. Danielson and C. D. Whittenberg, xe2x80x9cGuided Wave Reflectometry With Micrometer Resolutionxe2x80x9d, Appl. Opt. 26, 2836 (1987). The clear advantage of OCDR over OCT for the purpose of the invention is that it is a simpler and cheaper technique.
Besides light having a wavelength at or near 670 nm, as disclosed by L. S. Matchette of the Center for Devices and Radiological Health, of the US Food and Drug Administration, at the 13th International Congress on Photobiology in San Francisco, Calif., light having a wavelength of 1300 nm also appears to be suitable for use with the above-mentioned optical techniques. Since the latter wavelength is also used in the ICT sector, there is no or only a limited need for developing suitable optical components.
It is further possible to use spatially resolved diffuse reflectance spectroscopy which is described, for example, in J. T. Bruulsema et al., xe2x80x9cCorrelation between Blood Glucose Concentration in Diabetics and Noninvasively Measured Tissue Optical Scattering Coefficientxe2x80x9d, Opt. Lett. 22, 190 (1997).
Alternatively, the light reflection of the skin is measured during step C), since also the light reflection is correlated with the MED as described in EP 0 238 574 B 1. However, the correlation between the light reflection of the skin and MED appears to be less accurate than the correlation between the light attenuation in the skin and MED. By combining the knowledge of the correlation between the light reflection of the skin and MED and the correlation between the attenuation of the skin and MED it is possible to predict the MED even more accurately. The accuracy of the determination of the MED is expected to increase even further when the measurement is combined with other measured parameters that are known to correlate with the skin""s UV sensitivity, such as pigmentation and epidermal thickness. These parameters can also be measured non-invasively.
Preferably, a safe sunbathing time is electronically calculated on the basis of the deduced MED and of a relevant, preferably measured, solar UV radiation level. Information about the electronically calculated safe sunbathing time may be used by a user of a tanning-related device in order to maximize his tanning without the risk of inducing visible redness of the skin.
Another use of the electronically calculated safe sunbathing time may be the automatic turning-off of a solarium as soon as a time period has elapsed corresponding to the safe sun-bathing time since the moment the solarium was turned on.
Another advantageous possible use may be with a dosimeter, for example a solar watch, which measures the solar UV radiation level and warns the user of the dosimeter with a signal as soon as the user""s personal MED has been reached, in other words when the safe sunbathing time has elapsed.
According to another aspect of the present invention, a device is provided for use with a tanning-related device.
As indicated above, tanning-related devices, such as solaria, are operated in practice on the basis of an estimated classification of the user""s skin type, which has all the disadvantages mentioned above. It is therefore an object of the invention to provide a device which objectively, accurately, and non-invasively gives a user of a tanning-related device information about his MED.
According to a second aspect of the present invention, a device for use with a tanning-related device is provided comprising measuring means for non-invasively measuring a feature of the person""s skin related to the person""s personal MED, deduction means for deducing the person""s personal MED from the measured feature, and communicating means for electronically communicating a signal representing the deduced MED to a tanning-related device.
Advantageously, the device is provided with a timer for giving a warning signal, for instance a sound or light signal, as soon as a time period corresponding to the safe sunbathing time has elapsed. This allows the user of the device to relax fully without worrying that he will develop visible skin redness, because he will be warned just before this would occur.
According to a third aspect of the present invention, a tanning-related device, for example a solarium, comprising a device as described above is provided. This has the clear benefit that the user of the tanning-related device always has at his disposal the possibility of accurately and non-invasively determining his MED which gives him the benefits as described above.
By providing a tanning-related device with a switch which can start a timer and at the same time the tanning-related device itself, and which furthermore switches off the tanning-related device upon receipt of a warning signal of the timer as soon as the safe sunbathing time has elapsed, there will be no risk of his skin becoming red.